<style is="custom-style">
  :root {
    --cs-blue: {
      border : 8px solid blue;
    };
  }
</style>
<dom-module id="x-client">
  <template>
    <style>
      :host {
        display: inline-block;
        border : 4px solid red;
        @apply (--cs-blue);
      }
    </style>
    x-client
  </template>
  <script>
    Polymer({
      is: 'x-client'
    });
  </script>
</dom-module>
